| 摘要 |
PROBLEM TO BE SOLVED: To provide an output circuit of a radio-frequency transmitter in which a noise output power outside a signal band at the time of maximum power output is suppressed and degradation in communication quality within a low gain region is suppressed. SOLUTION: The output circuit of a radio-frequency transmitter includes a fine tuning variable gain amplifier which amplifies the signal of first frequency, a rough tuning variable gain amplifier which amplifies the signal that has a second frequency being higher than the first frequency and is produced by up-converting the frequency of the output signal, and a gain control unit for controlling raising/lowering the entire gain between minimum gain and maximum gain by raising/lowering the gain of the rough tuning variable gain amplifier by its variable width each time the gain of the fine tuning variable gain amplifier is raised/lowered within the gain variable range. The gain control unit controls the maximum gain in the gain variable range of the fine tuning variable gain amplifier when the gain of the rough tuning variable gain amplifier is controlled to be a minimum gain range, to be lower than the maximum gain in the gain variable range of the fine tuning variable gain amplifier when the gain of the rough tuning variable gain amplifier is controlled to be a maximum gain range. COPYRIGHT: (C)2010,JPO&INPIT
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